The present invention relates to communication systems in general, and in particular to communication systems that transmit telephone signals over compressed computer networks.
As an alternative to placing all telephone calls through the public switched telephone network, many companies are utilizing the excess capacity in their computer networks to carry a portion of their telephone calls. This is advantageous because the company does not have to pay for each telephone call individually. However, because such networks were not specifically designed for telecommunication, there are some inherent problems that occur when transmitting telephone signals over such networks.
One common problem with telephone calls that are routed over computer networks occurs when a call is placed to a system or device that detects and responds to dual tone multi-frequency (DTMF) signals commonly referred to as Touch-tone(trademark) signals. Such systems may include voice mail systems that allow users to store and retrieve messages or voice recognition units (also called integrated voice response units) that are programmed to retrieve information after entering one or more Touch-tone signals on a telephone keypad. One example of a voice recognition unit is an automatic banking response system of the type commonly provided by banks to allow users to access their accounts over the telephone.
When telephone signals are transmitted over a computer network, such as a local area network (LAN) or wide area network like the Internet, the telephone voice signals, as well as the DTMF signals are digitized, organized into a number of data packets, and compressed prior to transmission. Upon receipt, these data packets are decompressed and analyzed to reconstruct the original telephone signals. When a DTMF signal is compressed, transmitted over the computer network, and decompressed, the result is no longer a set of pure sinusoidal tones having predefined frequencies. Instead, the tones become distorted and can therefore be difficult to detect with a digital signal processor. As such, many communication systems do not support sending DTMF signals over compressed computer networks. Alternatively, systems are required to store the telephone number of the voice mail or integrated voice response systems that can be accessed within a network. All calls to these systems are routed over uncompressed networks. The complexities of routing a call on either an uncompressed or compressed network, depending on the destination, is generally inefficient.
Given the shortcomings in the prior art, there is a need for a method of reliably sending DTMF signals over compressed computer networks that does not require the use of additional channels or monitoring the destination called.
The present invention is a method of transmitting DTMF signals over a computer network. A received telephone signal is digitized, divided into a series of packets, and compressed using a conventional compression algorithm. The compressed packets are then transmitted on a data network. As the telephone signal is being digitized and divided into packets, it is continually analyzed to detect the presence of a DTMF signal. Upon the detection of a DTMF signal, an additional confirmation packet is inserted into the stream of packets and transmitted after the compressed packet that represents the DTMF signal. According to one embodiment of the invention, the confirmation packet comprises the uncompressed DTMF signal.
At a receiving end, packets are decompressed and analyzed to determine if they may represent a DTMF signal. If it appears that a packet containing a compressed version of a DTMF signal has been received, a receiving station looks for the confirmation packet. If the confirmation packet is present, the receiving station knows that a DTMF signal was received and the DTMF signal is processed accordingly. If the confirmation packet is not detected, then the compressed packet in question is treated as a voice signal.
According to another embodiment of the present invention, a telephone signal to be transmitted over a computer data network is simultaneously compressed and analyzed for the presence of a DTMF signal. If a DTMF signal is detected, a confirmation packet comprising a code that represents the DTMF signal is produced. The code representing the DTMF signal and the compressed telephone voice signals are transmitted on separate virtual channels of the same logical channel to a receiver over a computer network.
In another embodiment of the invention, a multiplexer receives the output of a speech compressor and a DTMF signal detector and transmits one or more codes representing DTMF signals on separate virtual channels of a single real time protocol data stream.